It is known in the field of automated milking to use optical sensors to determine the attitude and location in three dimensions of the teats in order to guide the milking apparatus. Laser-based optical triangulation sensors are used to image the teats and to derive their position in three dimensions. Light is projected into the field of view and the reflected light is imaged on a camera that lies in the projection plane. The optics as well as the light source are housed in a sensor enclosure, the size of which must accommodate the optics involved.
The enclosure is typically mounted on a robot arm that is manipulated to obtain an unobstructed field of view of the various teats involved. The robot arm must be engineered to accommodate the weight and size of the sensor. The sensor seeks to image a relatively small area between the belly of the animal and the top of the milking cups. Given the size of the sensor housing, this provides a limited range of movement, which imposes a constraint on the quality of the images that can be obtained, particularly when one teat obstructs another.
Two teats at different distances but whose images overlap may, depending on the angle of the camera, appear to be at the same distance. Manipulation of the camera to acquire images from several angles may be necessary to discriminate between teats in such cases. This is a significant problem. Moreover, either of the field of view or the projected light might be obstructed.
In addition to needing to obtain an unobstructed view of the various teats, when several teats are at both different distances and different angles from the sensor, inaccuracies may also arise in assessing the location of the teats by triangulation. Manipulation of the robot arm can partially compensate for this, but additional computation is required to accurately assess distance.
In order to attach the milking cups to the teats, it is critical to obtain the orientation and location of the tips of the teats in 3D space. Triangulation devices achieve this by using the robot arm to move them around and analyze the results from successive scans. But the animal and its teats are not stationary but rather are in motion during the scanning. This results in unreliable determination of the absolute location and orientation of the teats.
One means of accommodating the movement of the animal is to image the hind legs and to assume that the movement of the hind legs approximates the movement of the teats. However that approach is of limited usefulness due to the limited depth of field of current optical triangulation systems.
Stereo imaging systems also face similar problems. Both cameras must image the same teat at the same time but the use of two cameras increases the risk of a teat being obscured by another at one of the cameras.
Ultrasonics-based sensing systems that are sometimes used in milking applications measure the time of flight of sound waves. The footprint of the sound waves drastically limits spatial resolution. In addition, the speed of sound is influenced by air temperature and humidity and airflow speeds, and echoing adds noise which must be accommodated in the processing of the image.
It is an object of the present invention to provide a teat sensing system in an automated milking system that overcomes the aforementioned disadvantages and that is compact, easy to manipulate and effective.
The objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows.